In a typical circuit network, a terminal may use a circuit-level control message to use mandatory supplementary services related to telephony such as caller identification display service and call waiting service.
However, the terminal which allows receiving voice call services through Voice over LTE (VoLTE) in a packet network has to connect to an XML Configuration Access Protocol (XCAP) server to configure such supplementary services. The XCAP standard technology is a technology allowing a client to register application-specific user configuration information with the XCAP server and manage the registered information directly.
The application-specific user configuration information stored in the XCAP server is written in eXtensible Markup Language (XML), and the XCAP client connects to the XCAP server using Hypertext Transfer Protocol (HTTP) 1.1. That is, the VoLTE terminal has to receive an XCAP message to perform IP data transmission other than control message to configure supplementary service configuration.
In an exemplary LTE network, the terminal connects to a Packet Data Network (PDN) with an Access Point Name (APN) configured by the network. The PDN may be an Internet PDN for access to Internet, operator PDN for access to an operator network service, or IP Multimedia Subsystem (IMS) PDN for access to an IMS network service. In the case of VoLTE, it is possible to connect to the IMS PDN through an IMS APN determined by the operator. The VoLTE terminal transmits the call establishment control message, i.e. SIP signaling message, to the IMS PDN and the XCAP message to the Internet PDN.
In the case that the terminal is roaming, it is typical to allow only voice service roaming but not data service roaming. It is also possible to assume a situation where only the voice service is allowed without connection to the data service. In this case, the roaming network allows the connection with the IMS APN of the roaming terminal but not the connection to an Internet APN. That is, although the IMS SIP signal message is delivered to the IMS PDN of the home network, the XCAP message as normal Internet traffic cannot be delivered.
If the roaming network allows connection to the Internet APN for transmitting the XCAP message, this may cause extra Internet traffic in addition to the XCAP message (e.g. automatic updates of Internet connection applications), resulting in unintended cost. There is therefore a need of a method and apparatus allowing a terminal to transmit the message for use in the Internet connection such as XCAP message in an environment in which the terminal cannot connect to the Internet.